This invention relates to deflection circuits for television receivers, for example.
In many horizontal deflection circuits, the deflection winding is series coupled with an "S" shaping capacitor that is charged to a DC voltage. A trace switch, such as a horizontal output transistor and a parallel damper diode, is coupled across this series arrangement. When the trace switch closes during the trace interval, the DC voltage developed across the deflection winding generates a sawtooth trace current in the winding.
A primary winding of a flyback transformer is coupled between a voltage supply terminal and the horizontal output transistor collector electrode. During trace, current flows in the primary winding, storing energy in the winding magnetic field, which is then transferred to load circuits coupled to the flyback transformer, such as the high voltage ultor, during retrace when the deflection winding and a retrace capacitor go through one-half cycle of resonant oscillation.
Because the trace switch is coupled to the flyback primary winding, the reflected DC load current flowing in the primary winding causes the collector current in the horizontal output transistor to be increased at the end of trace. More base drive is required to maintain the transistor in saturation.
Also with the primary winding coupled to a voltage supply, such as a rectified AC line mains voltage, the output stage of the horizontal deflection circuit is not electrically isolated from the supply. It is desirable to isolate as many of the television receiver circuits as feasible to further reduce electrical shock hazard.